Thermoelectric material is one of the simplest technologies for energy conversion. Through conduction electrons of thermoelectric material, heat energy transfer to electrical power or move from cold side to hot side in a non-mechanical manner. Therefore, thermoelectric material has the potential for applying in cogeneration, portable electric power and air-conditions system.
The energy conversion efficiency of a thermoelectric material is closely related to the dimensionless thermoelectric figure of merit ZT. The thermoelectric figure of merit ZT=S2σ/k, wherein S is a Seebeck coefficient, σ is an electrical conductivity, and k is a thermal conductivity. With increasing performance of the thermoelectric material, the efficiency of a thermoelectric cooler or a thermoelectric power generator will be increased. Conventional thermoelectric materials, have been developed from 1960's, is limited to ZT=1.0 at room temperature. Currently, many researches focus on the development of thermoelectric material with nanostructure and ZT got important breakthrough to 1.5 to 2.0.
A high performance thermoelectric material is with high Seebeck coefficient, high electrical conductivity and low thermal conductivity. Since an increase in Seebeck coefficient normally implies with a decrease in electrical conductivity. Increasing carrier concentration means an increment of electrical conductivity and implies the decreasing in Seebeck coefficient and increasing in thermal conductivity. Therefore, the material is intrinsically with the limitation of ZT value.
To enhance the thermoelectric figure of merit, the main research focuses on the development of nanostructurenanostructurenano composite thermoelectric material which having a small energy band gap. That is, the optimization between the Seebeck coefficient, thermal conductivity and electrical conductivity is obtained by changing the dopant, doping level and the nanostructure of the material, so as to achieve the maximum thermoelectric figure of merit value.